1. Field of the Invention
The present invention relates to a gas laser oscillator which controls the adjusted level of a laser power supply.
2. Description of the Related Art
To drill high grade holes or stably cut a workpiece, an induction discharge excitation type gas laser oscillator is used. A gas laser oscillator mainly includes a plurality of discharge tubes through which a laser gas circulates, a plurality of main discharge electrodes which are arranged corresponding to the plurality of discharge tubes and make main discharge start for discharge excitation of the laser gas, and a plurality of auxiliary electrodes which are arranged adjoining the plurality of main discharge electrodes and make auxiliary discharge start in the laser gas in a state lower than the output at which main discharge starts.
In this connection, FIG. 3A to FIG. 3C are views which show the relationship X between the command voltage and discharge tube voltage. In these figures, the abscissa shows a command voltage to a laser power supply, while the ordinate shows the voltage of the discharge tubes.
In FIG. 3A, the discharge tube voltage linearly increases sharply from 0 kV until the point P and, when reaching the point P, linearly increases gradually. This point P corresponds to the main discharge extinction level V1. If the discharge tube voltage is smaller than this value, the main discharge extinguishes. When the discharge tube voltage exceeds the main discharge extinction level V1, the main discharge is started and the laser is output. As will be understood from FIG. 3A, the auxiliary discharge extinction level V2 is smaller than the main discharge extinction level V1.
In this connection, a command which is necessary for maintaining auxiliary discharge in the state where the laser output is 0 W will be called a “base discharge command”. In FIG. 3A, the base discharge command is adjusted in the zone Z1 between the main discharge extinction level V1 and the auxiliary discharge extinction level V2. Further, the laser output command, which is determined in accordance with the laser power which the gas laser oscillator demands, is added to the base discharge command and output from the output command device to the laser power supply.
If the gas laser oscillator cools and for example the laser gas temperature falls from 7° C. to about 47° C., as shown in FIG. 3B by the broken line, the relationship X shifts in the upward direction. Along with this, the main discharge extinction level V1 and the auxiliary discharge extinction level V2 respectively rise to the main discharge extinction level V1max and the auxiliary discharge extinction level V2max. For this reason, when setting the base discharge command to the auxiliary discharge extinction level V2, the auxiliary discharge may extinguish.
In such a state, if the command voltage to the laser power supply is increased, a situation can arise where impedance matching is not possible between the laser power supply and the discharge load. As a result, a large voltage is applied to the discharge tubes, excessive current flows to the laser power supply, and the discharge tubes and laser power supply may break.
As opposed to this, if the gas laser oscillator is warm and for example the laser gas temperature becomes 127° C. or more, as shown in FIG. 3C by the one-dot chain line, the relationship X shifts in the downward direction. Along with this, the main discharge extinction level V1 and the auxiliary discharge extinction level V2 respectively fall to the main discharge extinction level V1min and the auxiliary discharge extinction level V2min. When the main discharge extinction level V1 falls down to the main discharge extinction level V1min, even if the laser output is controlled to become 0 W, the main discharge is prevented from extinguishing.
In such a state, if opening the mechanical shutter which is provided at the front of the output mirror of the gas laser oscillator, laser light is unnecessarily output to the workpiece and the workpiece surface may be damaged. Normally, the speed of opening and closing of the mechanical shutter is relatively slower by about several seconds, so the adjusted level of the base discharge is set so that such processing defects do not arise. Setting such an adjusted level of the base discharge will be called an “electric shutter”. An electric shutter is also disclosed in Japanese Patent No. 3157470 and Japanese Patent Publication No. 58-155643A.
However, the adjusted level for maintaining auxiliary discharge and the adjusted level for realizing the electric shutter are in a mutually opposite relationship. Therefore, even if the gas laser oscillator is cold, it is difficult to maintain the auxiliary discharge and even if the gas laser oscillator is warm, it is also difficult to realize an electric shutter.
Further, in Japanese Patent No. 3157470, in the instant when making the laser output command zero, it is necessary to lower the base discharge command by exactly a predetermined value. Furthermore, the laser output command and the base discharge command which are transmitted from the CNC to the communication use IC are asynchronous and the delay times of the processing circuits thereof also differ. For this reason, a circuit for obtaining synchronization, for example, a latch circuit, becomes necessary. The cost increases and the processing of the software for control becomes complicated.
Furthermore, when the laser output command and the base discharge command cannot be perfectly synchronized, the commands become discontinuous. As a result, processing defects of the workpiece may occur. Further, in Japanese Patent No. 3157470, the base discharge command is made to descend from a predetermined value to realize an electric shutter. For this reason, depending on the amount of drop or the time setting, sometimes the effect of the electric shutter cannot be obtained or the auxiliary discharge may extinguish.
Further, in the configuration of Japanese Patent Publication No. 58-155643A, a power source for main discharge and a power source for auxiliary electrode use are provided. These are independently controlled. In this case, there are the problems that it is necessary to separately prepare a power source for auxiliary electrode use and the cost increases.
The present invention was made in consideration of such a situation and has as its object the provision of a gas laser oscillator which maintains auxiliary discharge even in a cold state while able to realize an electric shutter even in a warm state.